Continuous and pulsed voltage stressmg of metal oxide semiconductor (MOS)
transistors and capacitors has been mvestigated. The expenmental work followed a
survey of failure mechanisms in semiconductor devices which Identified Electrical
Overstress Damage (EOS)/Electrostatic Discharge (ESD) damage as the most
frequent cause of failure, accounting for over 50% of all damage observed. The
survey itself, covered all aspects of semiconductor reliability including reliability
modelling and quality assurance.
A qualitative model of oxide breakdown in MOS structures was developed as a
result of the experimental work. Two different mechanisms have been proposed for
continuous and pulsed voltage breakdown. Continuous voltage breakdown simulating EOS conditions, was temperature and
voltage dependent. The long time-scales involved, lead to a model whereby
breakdown IS the result of conduction of charge earners through the oxide, via
electron traps and impunty Sites with energies m the forbidden gap. Pulsed voltage
breakdown simulating ESD, was voltage dependent but not temperature dependent.
The very short time-scales involved indicate that breakdown is the direct result of
electron transport m the oxide conduction band. Electrons are inJected into the
conduction band via quantum-mecharucal tunnelling from the cathode.
Both mechanisms were found to be dependent on the surface charge concentratiOn
of the Silicon and, therefore, polanty dependent. The models explain this effect by
analysing the charge injection process under high electric fields.

Description:

A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.